<div class="demo">
<h1>shop works!</h1>
<h1>一个最基本的单例服务</h1>
<button (click)="add('abc')">新增</button>
<button (click)="dellast()">删除最后一个</button>
<button (click)="reload()">刷新</button>
<hr>
<ul *ngFor="let each of lst">
  <li>{{each}}</li>
</ul>
</div>
